Photographic illumination device, image-capturing system, camera system and camera

ABSTRACT

An image-capturing system includes: an image-capturing device that captures an image of a subject; and an illumination device that illuminates the subject. The image-capturing device includes a control unit that calculates a light quantity needed to illuminate the subject based upon at least, either an exposure time or an aperture value and image-capturing sensitivity. The illumination device includes a current-controlled light emission unit that emits light used to illuminate the subject and a light emission control unit that controls the light emission unit so as to emit light in the light quantity calculated by the control unit.

This is a Continuation of application Ser. No. 11/000,429 filed Dec. 1,2004, which claims the benefit of Japanese Patent Application No.2003-407500 filed Dec. 5, 2003. The disclosure of the prior applicationsis hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination device used toilluminate a main subject during a photographing operation, animage-capturing system, a camera system and a camera.

2. Description of the Related Art

There is a camera known in the related art that illuminates a mainsubject with an illumination device that uses an LED-type instead of adischarge-type illumination device such a xenon discharge tube (seeJapanese Laid Open Patent Publication No. 2002-207236). In the cameradisclosed in Japanese Laid Open Patent Publication No. 2002-207236, thequantity of light to be emitted from the illumination device isdetermined based upon the subject distance measured by a range findingdevice and the film sensitivity. The publication discloses that thelight quantity is controlled by varying the number of LEDs driven, thevalue of the electrical current which drives the LEDs and the length oftime over which the LEDs emit light.

SUMMARY OF THE INVENTION

There is a concern that overexposure or underexposure may occur during adaylight synchronous (fill-in flash) photographing operation or a slowsynchronous photographing operation unless the photographing operationis performed by taking into consideration the shutter speed and theaperture value.

According to the 1st aspect of the invention, a photographicillumination device comprises: a current-controlled light emission meansthat emits illuminating light toward a subject; a range finding meansthat detects distance information indicating a distance to a mainsubject; and a light emission control means that controls the lightemission means to emit light in a quantity calculated by using thedistance information detected by the range finding means and an exposuretime, an aperture value and a photographic sensitivity set in a camera.

According to the 2nd aspect of the invention, a photographicillumination device comprises: a current-controlled light emission meansthat emits illuminating light toward a subject; and a light emissioncontrol means that controls the light emission means to emit light in aquantity calculated by using distance information indicating a distanceto a main subject which is detected by a range finding means in a cameraand an aperture time, an aperture value and a photographic sensitivityset in the camera.

According to the 3rd aspect of the invention, in the photographicillumination device according to the 1st aspect or the 2nd aspect, it ispreferred that the light emission control means continuously supplies adrive current to the light emission means over a specific length oftime.

According to the 4th aspect of the invention, in the photographicillumination device according to the 3rd aspect, it is preferred thatthe light emission control means gradually increases the drive current.

According to the 5th aspect of the invention, in the photographicillumination device according to the 1st aspect or the 2nd aspect, it ispreferred that the light emission control means supplies a pulse drivecurrent to the light emission means a specific number of times.

According to the 6th aspect of the invention, in the photographicillumination device according to any of the 3rd through 5th aspects itis preferred that the light emission control means stops supplying thedrive current once an integrated value representing light having beenreflected off the subject illuminated by the light emission meansbecomes equal to a value corresponding to the calculated light quantity.

According to the 7th aspect of the invention, in the photographicillumination device according to any of the 1st through 5th aspects, itis preferred that the light emission control means determines a level ofdrive current so as to sustain a supply of drive current to the lightemission means while exposure is in progress over the exposure time.

According to the 8th aspect of the invention, a camera system comprises:a photographic illumination device according to any of the 1st through7th aspects; and a camera having a range finding means that detectsdistance information indicating a distance to a main subject, anarithmetic operation means that calculates a quantity of light to beemitted by the light emission means by using the distance informationdetected by the range finding means and an exposure time, an aperturevalue and a photographic sensitivity set in the camera, and a signaloutput means that outputs a signal indicating the light quantitycalculated by the arithmetic operation means.

According to the 9th aspect of the invention, a camera comprises: acurrent-controlled light emission means that emits illuminating lighttoward a subject; a range finding means that detects distanceinformation indicating a distance to a main subject; an arithmeticoperation means that calculates a quantity of light to be emitted by thelight emission means by using the distance information detected by therange finding means and an exposure time, an aperture value and aphotographic sensitivity set therein; and a light emission control meansthat controls the light emission means to emit light in the calculatedlight quantity.

According to the 10th aspect of the invention, a camera systemcomprises: a current-controlled light emission means that emitsilluminating light toward a subject; an arithmetic operation means thatstarts a light emission at the light emission means in response to alight emission start signal and calculates a quantity of light to beemitted by the light emission means by using information indicating anaperture value and photographic sensitivity set therein; and a lightemission control means that controls a light emission quantity inconformance to the calculated light quantity.

According to the 11th aspect of the invention, a camera systemcomprises: a current-controlled light emission means that emitsilluminating light toward a subject; an arithmetic operation means thatstarts a light emission at the light emission means in response to alight emission start signal and calculates a quantity of light to beemitted by the light emission means by using distance information settherein and information corresponding to an aperture value andphotographic sensitivity set therein; and a light emission control meansthat controls a light emission quantity in conformance to the calculatedlight quantity.

According to the 12th aspect of the invention, a portable devicecomprises: a current-controlled light emission means that emitsilluminating light toward a subject; an arithmetic operation means thatstarts a light emission at the light emission means in response to alight emission start signal and calculates a quantity of light to beemitted by the light emission means by using information indicating anaperture value and photographic sensitivity set therein; and a lightemission control means that controls a light emission quantity inconformance to the calculated light quantity.

According to the 13th aspect of the invention, a portable devicecomprises: a current-controlled light emission means that emitsilluminating light toward a subject; an arithmetic operation means thatstarts a light emission at the light emission means in response to alight emission start signal and calculates a quantity of light to beemitted by the light emission means by using distance information settherein and information corresponding to an aperture value andphotographic sensitivity set therein; and a light emission control meansthat controls a light emission quantity in conformance to the calculatedlight quantity.

According to the 14th aspect of the invention, an image-capturing systemcomprises: an image-capturing device that captures an image of asubject; and an illumination device that illuminates the subject. Theimage-capturing device comprises a control means that calculates a lightquantity needed to illuminate the subject based upon at least, either anexposure time or an aperture value and image-capturing sensitivity. Theillumination device comprises a current-controlled light emission meansthat emits light used to illuminate the subject and a light emissioncontrol means that controls the light emission means so as to emit lightin the light quantity calculated by the control means.

According to the 15th aspect of the invention, an image-capturing systemaccording to the 14th aspect, it is preferred that the control means inthe image-capturing device calculates the light quantity based upon theexposure time, the aperture value and the image-capturing sensitivityset therein and measured subject brightness, so as to achieve optimalexposure.

According to the 16th aspect of the invention, an image-capturing systemaccording to the 14th aspect or the 15th aspect, it is preferred that:the image-capturing device further comprises a range finding means thatdetects distance information indicating a distance to the subject; andthe control means in the image-capturing device calculates the lightquantity by taking into consideration the distance informationindicating the distance to the subject.

According to the 17th aspect of the invention, in the image-capturingsystem according to any of the 14th through 16th aspects, it ispreferred that the light emission control means in the illuminationdevice controls light emission intensity at the light emission means incorrespondence to the exposure time.

According to the 18th aspect of the invention, in the image-capturingsystem according to the 17th aspect, it is preferred that the lightemission control means in the illumination device controls the lightemission intensity at the light emission means so as to emit light inthe light quantity over the exposure time.

According to the 19th aspect of the invention, in the image-capturingsystem according to the 18th aspect, it is preferred that the lightemission control means in the illumination device implements control soas to stop the light emission by the light emission means once light inthe light quantity has been emitted.

According to the 20th aspect of the invention, in the image-capturingsystem according to any of the 14th through 19th aspects, it ispreferred that the light emission control means in the illuminationdevice has information indicating drive current and light emissionintensity characteristics at the light emission means.

According to the 21st aspect of the invention, an illumination device isthe illumination device constituting the image-capturing systemaccording to any of the 14th through 20th aspects.

According to the 22nd aspect of the invention, a camera is a camerahaving the image-capturing device constituting the image-capturingsystem according to any of the 14th through 20th aspects.

According to the 23rd aspect of the invention, a camera corresponds tothe image-capturing system according to any of the 14th through 20thaspects.

According to the 24th aspect of the invention, a portable deviceequipped with a camera corresponds to the image-capturing systemaccording to any of the 14th through 20th aspects.

It is to be noted that the term “means” used above may be replaced with“unit”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the camera system achieved in a first embodiment ofthe present invention;

FIG. 2 is a block diagram of the structure in the essential portion ofthe electronic camera;

FIG. 3 is a block diagram of the structure adopted in the essentialportion of the externally mounted flash unit;

FIG. 4 shows the relationship between the length of current supplyperiod and the drive current which is determined by the illuminationcontrol circuit;

FIG. 5 shows the relationship between the length of current supplyperiod and the drive current achieved in an example of a variation;

FIG. 6 shows the relationship between the length of current supplyperiod and the drive current achieved in another example of a variation;and

FIG. 7A shows the interior surfaces of a portable telephone in an openstate; and

FIG. 7B shows the exterior surfaces of the portable telephone in an openstate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is an explanation of the preferred embodiments of thepresent invention, given in reference to the drawings.

First Embodiment

FIG. 1 illustrates the camera system achieved in the first embodiment ofthe present invention. FIG. 1 shows that an exchangeable photographiclens 20 is mounted at an electronic camera 10. In addition, anexternally mounted flash unit 30 is mounted at an accessory shoe (notshown) of the electronic camera 10.

FIG. 2 is a block diagram of the essential structure adopted in theelectronic camera 10. An arithmetic operation circuit 101 in FIG. 2 isconstituted with a microcomputer and the like. The arithmetic operationcircuit 101 executes specific arithmetic operations by using signalsinput thereto from the individual blocks to be detailed later andoutputs control signals generated based upon the results of thearithmetic operations to the various blocks. The arithmetic operationcircuit 101 further includes an interface circuit (not shown) whichenables communication with the external flash unit 30.

An image-capturing element 121 may be constituted with a CCD imagesensor or the like. The image-capturing element 121 captures an imageformed with subject light having passed through the photographic lens 20and outputs image-capturing signals to an A/D conversion circuit 122. Atthe A/D conversion circuit 122, the analog image-capturing signals areconverted to digital signals. The image-capturing element 121 and theA/D conversion circuit 122 are driven so as to engage in operations withspecific timing by drive signals output from a timing circuit 124.

An image processing circuit 123 is constituted with an ASIC and thelike. In addition to executing image processing such as white balanceprocessing on the image data resulting from digital conversion, theimage processing circuit 123 executes compression processing forcompressing the image data having undergone the image processing into aspecific format, decompression processing for decompressing thecompressed image data and the like. In a buffer memory 125, image datato be processed by the image processing circuit 123 are temporarilystored. A recording medium 126 is constituted with a memory card or thelike that can be detachably loaded into the camera. Image data havingundergone the image processing are recorded into the recording medium126.

A photometering device 111 detects the quantity of subject light havingpassed through the photographic lens 20 and outputs a detection signalto the arithmetic operation circuit 101. The arithmetic operationcircuit 101 calculates the subject brightness by using this detectionsignal. A photosensor 103 receives light having been emitted from theexternal flash unit 30 and reflected from the subject. The photosensor103 also outputs a time integral value obtained through time integrationof the light reception signal to the arithmetic operation circuit 101.

A focal point detection device 104 detects the state of the focal pointposition adjustment achieved with the photographic lens 20 and outputs adetection signal to the arithmetic operation circuit 101. A lens drivedevice 105 drives a focus lens (not shown) within the photographic lens20 forward/backward along the optical axis in response to a commandissued by the arithmetic operation circuit 101, so as to adjust theposition of the focal point of the photographic lens 20. It is to benoted that a detection signal provided by the focal point detectiondevice 104 constitutes distance information that corresponds to thedistance to the main subject.

At a display device 118, photographic information such as the shutterspeed and the aperture value is displayed in response to a commandissued by the arithmetic operation circuit 101.

A shutter release switch SW1 outputs a shutter release operation signalto the arithmetic operation circuit 101 by interlocking with adepression of a shutter release operation button (not shown).

A motor drive circuit 112 controls drive of a sequence motor 113 inresponse to a command issued by the arithmetic operation circuit 101.The sequence motor 113, which is part of a sequence drive device (notshown), raises/lowers a mirror (not shown), drives an aperture (notshown) and charges a shutter 115.

A sequence switch SW2, which is also part of the sequence drive devicementioned above, generates brake control timing for the sequence motor113 and the like.

A shutter drive circuit 114 individually controls holds on and releasesof a front curtain and a rear curtain (not shown) of the shutter 115. AnX contact point switch SW3 enters an on state and outputs an ON signalas a run of the front curtain at the shutter 115 is completed and entersan off state and outputs an OFF signal halfway through the charge of theshutter 115.

An aperture position detection device 116 detects the aperture positioncorresponding to the aperture value and outputs a detection signal tothe arithmetic operation circuit 101. An aperture lock device 117 stopsthe aperture being driven and locks the aperture at a specific aperturevalue.

A sensitivity setting operation member 120 outputs an operation signalcorresponding to an image-capturing sensitivity setting operation to thearithmetic operation circuit 101. Based upon the operation signal inputthereto, the arithmetic operation circuit 101 adjusts theimage-capturing sensitivity setting for the image-capturing element 121.The image-capturing sensitivity may be set in specific steps within arange equivalent to, for instance, ISO 100 through ISO 1600.

A shutter speed setting operation member 121 outputs an operation signalcorresponding to a shutter speed setting operation to the arithmeticoperation circuit 101. The arithmetic operation circuit 101 adjusts theshutter speed setting based upon the operation signal input thereto. Theshutter speed may be set in specific steps within a range of, forinstance, 1/8000 sec to 1 sec.

An aperture value setting operation member 122 outputs an operationsignal corresponding to an aperture setting operation to the arithmeticoperation circuit 101. The arithmetic operation circuit 101 adjusts theaperture value setting based upon the operation signal input thereto.The aperture value may be set in specific steps within a range of, forinstance, F 1.4 through F 22.

The arithmetic operation circuit 101 achieved in the present inventionexecutes an exposure calculation as expressed in (1) to (3) below byusing the current setting for the aperture value AV, the current settingfor shutter speed TV, the subject brightness BV calculated as describedearlier and the current setting for image-capturing sensitivity SV, whenthe camera is set to execute a photographing operation with lightemitted from the external flash unit 30.

EV=BV+SV  (1)

EV1=AV+TV  (2)

ΔEV=EV−EV1  (3)

EV in expression (1) represents the optimal exposure quantity. Thearithmetic operation circuit 101 calculates the optimal exposurequantity EV based upon the subject brightness BV and the image-capturingsensitivity SV. The exposure quantity EV1 in expression (2) is anexposure quantity determined in correspondence to the current aperturevalue setting AV and the current shutter speed setting TV. Namely, EV1is a control exposure quantity. Under normal circumstances, the valuesfor the aperture value AV and the shutter speed TV are set so as tomatch the control exposure quantity EV1 with the optimal exposurequantity EV. However, if the aperture value AV or the shutter speed TVis set in advance or if the aperture value AV or the shutter speed TVexceeds its limit value, the control exposure quantity EV1 and theoptimal exposure quantity EV may not match. It is to be noted that theoptimal exposure quantity and the control exposure quantity may besimply referred to as optimal exposure and control exposurerespectively.

The exposure deviation ΔEV in expression (3) represents the differencebetween the optimal exposure quantity EV and the control exposurequantity EV1. In order to achieve the correct exposure, the arithmeticoperation circuit 101 calculates the quantity of light to be emittedfrom the flash unit 30 in correspondence to the exposure deviation ΔEV.In other words, with the light emitted from the flash unit 30 in thequantity corresponding to the exposure deviation ΔEV which is calculatedby the arithmetic operation circuit 101, the optimal exposure quantityEV and the control exposure quantity EV1 can be made to match eachother. The arithmetic operation circuit 101 increases/decreases thequantity of light to be emitted based upon the distance informationindicating the distance to the main subject.

FIG. 3 is a block diagram of the essential structure adopted in theexternal flash unit 30. As shown in FIG. 3, the external flash unit 30includes an illumination control circuit 43, a DC/DC converter 40, LEDs(light emitting diodes) 41 and 42 and an interface circuit 9.

The DC/DC converter 40 is constituted of, for instance, an integratedcircuit used to drive the LEDS. The DC/DC converter 40 boosts a batteryvoltage supplied from a battery 1 via power lines L10 and L12 to avoltage achieving a predetermined voltage level (e.g., 3V) needed todrive the LEDs 41 and 42. In addition, the DC/DC converter 40 suppliesspecific levels of electric current to the LED 41 and the LED 42 inresponse to a command transmitted from the illumination control circuit43 via a signal line L11. The values representing the levels of thecurrent to be supplied to the LEDs 41 and 42 are determined by theillumination control circuit 43.

The LEDs 41 and 42 emit so-called white light. As is already known, anLED is a current-controlled device that manifests a proportionalrelationship between the drive current and the light emission intensity(light power) within its rated range. By controlling the drive currentsupplied to the LED 41 and the LED 42, the illumination control circuit43 controls the quantities of light emitted from the LEDs 41 and 42.

Once the external flash unit 30 is mounted at the accessory shoe (notshown) of the electronic camera 10, the arithmetic operation circuit 101in the electronic camera 10 becomes connected with the illuminationcontrol circuit 43 via the interface circuit 9. The signals that becomeconnected as a result include the X contact point signal from the Xcontact point switch SW3, the signal indicating the quantity of emittedlight and the signal indicating the shutter speed.

The X contact point signal is outputs to the illumination controlcircuit 43 while a signal output is allowed by the arithmetic operationcircuit 101 but is not output to the illumination control circuit 43 ifthe signal output is disallowed by the arithmetic operation circuit 101.

The illumination control circuit 43 is constituted with a microcomputerand the like. Upon receiving the signal indicating the quantity ofemitted light from the arithmetic operation circuit 101, theillumination control circuit 43 calculates the values of the drivecurrent needed to have illuminating light emitted from the LEDs 41 and42 in the quantity corresponding to the received signal and the lengthof current supply period (i.e., the length of time over which light isto be emitted). Namely, the quantity of light to be emitted is indicatedas the integrated value obtained by integrating the light emissionintensity over the length of time over which light is emitted. As an Xcontact point ON signal is input from the arithmetic operation circuit101, the illumination control circuit 43 issues an instruction for theDC/DC converter 40 indicating the drive current value and a lightemission start, and once the light emission period elapses, it issues aninstruction for a light emission stop.

The present invention is characterized by the drive current supplied tothe LEDs in order to enable the flash unit 30 to emit light in therequired quantity and the length of time over which the current issupplied in the camera system described above. In the first embodiment,light is emitted continuously at a constant light emission intensitylevel within the exposure time range corresponding to the shutter speedsetting.

FIG. 4 shows the relationship between the length of current supplyperiod and the drive current determined by the illumination controlcircuit 43. The horizontal axis and the vertical axis in FIG. 4respectively represent the length of current supply period and the drivecurrent. Upon receiving the signals indicating the quantity of light tobe emitted and the shutter speed (exposure time) from the arithmeticoperation circuit 101, the illumination control circuit 43 calculatesthe light emission intensity needed to achieve the indicated quantity ofemitted light through a light emission at a constant intensity levelduring the exposure and determines the drive current Ic needed toexecute the light emission at this light emission intensity level. Inthe example presented in FIG. 4, the length of current supply period Xcorresponds to the length of exposure time.

The relationship between the light emission intensity and the drivecurrent is stored in advance in a nonvolatile memory inside theillumination control circuit 43 as a table based upon the results of anactual measurement. The illumination control circuit 43 references thetable by using the light emission intensity level as an argument todetermine the value of the required drive current and outputs thecurrent value thus determined to the DC/DC converter 40.

Since there are two LEDs, the illumination control circuit 43 determinesthe drive current for each of the LEDs in the embodiment. It is to benoted that the sum of the quantities of light to be emitted by the LED41 and the LED 42 corresponds to the quantity of light to be emittedwhich is indicated by the arithmetic operation circuit 101.

The first embodiment explained above is now summarized.

(1) When the camera system is set for a photographing operation to beexecuted with light emitted from the external flash unit 30, theexposure calculation is executed by using the current aperture valuesetting AV, the current shutter speed setting TV, the detected subjectbrightness BV and the current image-capturing sensitivity setting SV,and the control exposure which includes the quantity of light to beemitted from the flash unit 30 is calculated in correspondence to thedifference ΔEV between the control exposure and the optimal exposure inorder to achieve the optimal exposure. As a result, accurate exposurecontrol can be implemented regardless of whether the shutter speed ishigh or low.(2) The LEDs 41 and 42 which are current-controlled devices are used aslight emitting elements in the flash unit 30, and thus, unlike in anillumination device using a discharge type light emitting tube such as axenon tube, no high-voltage circuit is required. Furthermore, light canbe continuously emitted at a constant intensity level over a specificlength of time. As a result, the cost of the drive circuit is reduced,the light emission can start without having to allow for any preparatorytime period (for charging and the like), and light can be emittedcontinuously during the exposure even when the shutter speed is low.(3) Since the flash unit 30 is allowed to emit light continuously withinthe exposure time range corresponding to the shutter speed setting, thelight emission intensity level can be lowered. Thus, the extent of glaremanifesting during a short-range photographing operation is not aspronounced as that experienced when light is emitted at a high level oflight emission intensity only over part of the exposure time. Inaddition, by emitting light continuously during a low speedphotographing operation, raindrops, flowing water and the like in thesubject can be represented for example.(4) Since the relationship between the light emission intensity and thedrive current is stored in a nonvolatile memory in the illuminationcontrol circuit 43 as a table, the quantity of light to be emitted canbe controlled with a high degree of accuracy even if the current lightemission intensity characteristics among individual LED are notconsistent. In addition, even if the current light emission intensitycharacteristics of the LED 41 are different from those of the LED 42,light emission can be controlled so as to match the levels of lightemission intensity at the two LEDs.

While two LEDs are utilized in the example explained above, the numberof LEDS is not limited to two, and a single LED or five LEDs may be usedinstead.

Within the range of exposure time corresponding to the shutter speed,setting, the intensity of light emission can be gradually raised duringthe continuous light emission. FIG. 5 shows the relationship between thelength of current supply period and the drive current determined by theillumination control circuit 43 in such a variation. In FIG. 5, thehorizontal axis represents the length of current supply period and thevertical axis represents the drive current. Upon receiving the signalsindicating the quantity of light to be emitted and the shutter speed(exposure time) from the arithmetic operation circuit 101, theillumination control circuit 43 calculates a light emission intensitypattern with which the indicated quantity of emitted light can beobtained by gradually increasing the light emission intensity during theexposure and then determines the drive current (including the currentincrease rate and the length of current supply period) needed to achievethis light emission intensity pattern. In the example presented in FIG.5, the length of current supply period Y corresponds to the length ofexposure time and the current value at the light emission start is Ig.

While the drive current is increased at a constant rate in FIG. 5, theincrease rate may be altered over time instead.

In addition, within the range of exposure time corresponding to theshutter speed setting, the required quantity of emitted light may beobtained through repeated pulse light emissions. FIG. 6 shows therelationship between the length of current supply period and the drivecurrent determined by the illumination control circuit 43 in such avariation. In FIG. 6, the horizontal axis represents the length ofcurrent supply period and the vertical axis represents the drivecurrent. Upon receiving the signals indicating the quantity of light tobe emitted and the shutter speed (exposure time) from the arithmeticoperation circuit 101, the illumination control circuit 43 calculates alight emission intensity pattern with which the indicated quantity ofemitted light can be obtained through repeated pulse light emissionsexecuted during the exposure and then determines the drive current(including the pulse current and the number of pulses) needed to achievethis light emission intensity pattern. In the example presented in FIG.6, the length of current supply period Z corresponds to the length ofexposure time and pulse light is emitted n times with the drive currentIp.

Second Embodiment

In the second embodiment, a time integral value provided by thephotosensor 103 after a light emission starts at the flash unit 30 ismonitored and the light emission at the flash unit 30 is stopped oncethe time integral value becomes equal to the required quantity of lightto be emitted within the range of exposure time corresponding to theshutter speed setting.

Upon receiving the signal indicating the quantity of light to be emittedfrom the arithmetic operation circuit 101, the illumination controlcircuit 43 calculates the values of the drive current and the length ofcurrent supply period (i.e., the length of time over which light is tobe emitted) needed to have illuminating light emitted from the LEDs 41and 42 in the quantity corresponding to the received signal. Then, inresponse to an X contact point ON signal input from the arithmeticoperation circuit 101, the illumination control circuit 43 issues aninstruction indicating the drive current and a light emission start tothe DC/DC converter 40. The operation of the illumination controlcircuit executed up to this point is identical to that in the firstembodiment.

Upon judging that the time integral value provided by the photosensor103 has reached a decision-making threshold value, the arithmeticoperation circuit 101 issues an instruction for the illumination controlcircuit 43 to stop the light emission. The decision-making thresholdvalue corresponds to the quantity of light to be emitted determinedthrough the exposure calculation. In this situation, the illuminationcontrol circuit 43 outputs a command for the DC/DC converter 40 to stopthe light emission at the LED 41 and the LED 42 even if the exposuretime is not up yet. It is to be noted that if the time integral valueprovided by the photosensor 103 does not reach the decision-makingthreshold value, an instruction for a light emission stop is issued oncethe originally calculated length of current supply period (whichcorresponds to the length of exposure time) elapses.

In the second embodiment explained above, the light having been emittedfrom the flash unit 30 to illuminate the main subject and having beenreflected off the main subject is monitored in real-time, and if thetime integral value of the reflected light becomes equal to a valuecorresponding to the required quantity of light to be emitted, thesupply of the drive current to the LED 41 and the LED 42 is stopped. Asa result, over exposure attributable to the illuminating light isprevented.

The second embodiment explained above may be adopted in any of the threeapplications described earlier; 1) when continuously emitting light at aconstant light emission intensity within the range of exposure timecorresponding to the shutter speed setting (FIG. 4), 2) when graduallyincreasing the light emission intensity during a continuous lightemission (FIG. 5) and 3) when repeatedly executing pulse light emission(FIG. 5).

Third Embodiment

In the third embodiment, the quantity of light to be emitted iscalculated in advance at the arithmetic operation circuit 101 based uponthe distance information that have been obtained, the aperture valueinformation and the photographing sensitivity information, and the LEDs41 and 42 emit light at the intensity level over the length of time bothdetermined by the arithmetic operation circuit. The third embodimentallows the light emission intensity level at the light emission start tobe set at an appropriate value. Since other features of the thirdembodiment are identical to those of the first embodiment, theirexplanation is omitted.

Fourth Embodiment

The photosensor 103 receives light reflected off the subject illuminatedwith light emitted from the LEDs 41 and 42 which starts the lightemission based upon the aperture value information and the photographicsensitivity information in response to a light emission start signal,and the light emission is stopped once an optimal value is achieved inthe fourth embodiment. As in the third embodiment, the light emissionintensity level at the light emission start can be set to an appropriatevalue in the fourth embodiment. Since other features are identical tothose in the first embodiment, their explanation is omitted.

While an explanation is given above on an example in which the presentinvention is adopted in conjunction with the external flash unit 30, aflash unit may instead be built into a camera main unit or a portabledevice such as a portable telephone.

In addition, while the distance is measured by the electronic camera 10,the information indicating the distance to the subject may instead bedetected by the flash unit 30, or such information may be obtained inadvance as data.

The exposure calculation may be executed at the flash unit 30 as well.In such a case, information indicating the aperture value and theshutter speed set in the camera is provided to the flash unit 30 fromthe camera through communication between the arithmetic operationcircuit 101 and the flash unit 30.

While an explanation is given above on an example in which the presentinvention is adopted in an electronic camera, the present invention mayalso be adopted in conjunction with a film camera or a portable devicesuch as a portable telephone (a cellular phone). FIGS. 7A and 7B showhow the present invention may be adopted in a portable telephone. FIG.7A shows the interior surfaces of a portable telephone 201 in an openstate, whereas FIG. 7B shows the exterior surfaces of the portabletelephone 201 in an open state. The portable telephone 201 includes acamera unit 202 and an illumination unit 203.

It is to be noted that the individual components described above may bealternatively referred to as follows. The LEDs 41 and 42 may be referredto as means for light emission. The focal point detection device 104 maybe referred to as a means for range finding. The illumination controlcircuit 43 may be referred to as a means for light emission control. Thearithmetic operation circuit 101 may be referred to as a means forarithmetic operation and also as a means for signal transmission.

The above described embodiments are examples and various modificationscan be made without departing from the spirit and scope of theinvention.

1. A photographic illumination device, comprising: a current-controlledlight emission unit that manifests a proportional relationship between adrive current and a light emission intensity and emits illuminatinglight toward a subject; a range finding unit that detects distanceinformation indicating a distance to a main subject; and a lightemission control unit that controls the light emission unit to emitlight in a quantity calculated by using the distance informationdetected by the range finding unit and an exposure time, an aperturevalue and a photographic sensitivity set in a camera.
 2. A photographicillumination device, comprising: a current-controlled light emissionunit that manifests a proportional relationship between a drive currentand a light emission intensity and emits illuminating light toward asubject; and a light emission control unit that controls the lightemission unit to emit light in a quantity calculated by using distanceinformation indicating a distance to a main subject which is detected bya range finding unit in a camera and an aperture time, an aperture valueand a photographic sensitivity set in the camera.
 3. A photographicillumination device according to claim 1, wherein: the light emissioncontrol unit continuously supplies a drive current to the light emissionunit over a specific length of time.
 4. A photographic illuminationdevice according to claim 3, wherein: the light emission control unitgradually increases the drive current.
 5. A photographic illuminationdevice according to claim 1, wherein: the light emission control unitsupplies a pulse drive current to the light emission unit a specificnumber of times.
 6. A photographic illumination device according toclaim 3, wherein: the light emission control unit stops supplying thedrive current once an integrated value representing light having beenreflected off the subject illuminated by the light emission unit becomesequal to a value corresponding to the calculated light quantity.
 7. Aphotographic illumination device according to claim 1, wherein: thelight emission control unit determines a level of drive current so as tosustain a supply of drive current to the light emission unit whileexposure is in progress over the exposure time.
 8. A camera system,comprising: a photographic illumination device according to claim 1; anda camera having a range finding unit that detects distance informationindicating a distance to a main subject, an arithmetic operation unitthat calculates a quantity of light to be emitted by the light emissionunit by using the distance information detected by the range findingunit and an exposure time, an aperture value and a photographicsensitivity set in the camera, and a signal output unit that outputs asignal indicating the light quantity calculated by the arithmeticoperation unit.
 9. A camera, comprising: a current-controlled lightemission unit that manifests a proportional relationship between a drivecurrent and a light emission intensity and emits illuminating lighttoward a subject; a range finding unit that detects distance informationindicating a distance to a main subject; an arithmetic operation unitthat calculates a quantity of light to be emitted by the light emissionunit by using the distance information detected by the range findingunit and an exposure time, an aperture value and a photographicsensitivity set therein; and a light emission control unit that controlsthe light emission unit to emit light in the calculated light quantity.10. A camera system, comprising: a current-controlled light emissionunit that manifests a proportional relationship between a drive currentand a light emission intensity and emits illuminating light toward asubject; an arithmetic operation unit that starts a light emission atthe light emission unit in response to a light emission start signal andcalculates a quantity of light to be emitted by the light emission unitby using information indicating an aperture value and photographicsensitivity set therein; and a light emission control unit that controlsa light emission quantity in conformance to the calculated lightquantity.
 11. A camera system, comprising: a current-controlled lightemission unit that manifests a proportional relationship between a drivecurrent and a light emission intensity and emits illuminating lighttoward a subject; an arithmetic operation unit that starts a lightemission at the light emission unit in response to a light emissionstart signal and calculates a quantity of light to be emitted by thelight emission unit by using distance information to a main subject settherein and information corresponding to an aperture value andphotographic sensitivity set therein; and a light emission control unitthat controls a light emission quantity in conformance to the calculatedlight quantity.
 12. A portable device, comprising: a current-controlledlight emission unit that manifests a proportional relationship between adrive current and a light emission intensity and emits illuminatinglight toward a subject; an arithmetic operation unit that starts a lightemission at the light emission unit in response to a light emissionstart signal and calculates a quantity of light to be emitted by thelight emission unit by using information indicating an aperture valueand photographic sensitivity set therein; and a light emission controlunit that controls a light emission quantity in conformance to thecalculated light quantity.
 13. A portable device, comprising: acurrent-controlled light emission unit that manifests a proportionalrelationship between a drive current and a light emission intensity andemits illuminating light toward a subject; an arithmetic operation unitthat starts a light emission at the light emission unit in response to alight emission start signal and calculates a quantity of light to beemitted by the light emission unit by using distance information to amain subject set therein and information corresponding to an aperturevalue and photographic sensitivity set therein; and a light emissioncontrol unit that controls a light emission quantity in conformance tothe calculated light quantity.
 14. An image-capturing system,comprising: an image-capturing device that captures an image of asubject; and an illumination device that illuminates the subject,wherein: the image-capturing device comprises a control unit thatcalculates a light quantity needed to illuminate the subject based uponat least, either an exposure time or an aperture value andimage-capturing sensitivity; and the illumination device comprises acurrent-controlled light emission unit that manifests a proportionalrelationship between a drive current and a light emission intensity andemits light used to illuminate the subject, and a light emission controlunit that controls the light emission unit so as to emit light in thelight quantity calculated by the control unit.
 15. An image-capturingsystem according to claim 14, wherein: the control unit in theimage-capturing device calculates the light quantity based upon theexposure time, the aperture value and the image-capturing sensitivityset therein and measured subject brightness, so as to achieve optimalexposure.
 16. An image-capturing system according to claim 14, wherein:the image-capturing device further comprises a range finding unit thatdetects distance information indicating a distance to the subject; andthe control unit in the image-capturing device calculates the lightquantity by taking into consideration the distance informationindicating the distance to the subject.
 17. An image-capturing systemaccording to claim 14, wherein: the light emission control unit in theillumination device controls light emission intensity at the lightemission unit in correspondence to the exposure time.
 18. Animage-capturing system according to claim 17, wherein: the lightemission control unit in the illumination device controls the lightemission intensity at the light emission unit so as to emit light in thelight quantity over the exposure time.
 19. An image-capturing systemaccording to claim 18, wherein: the light emission control unit in theillumination device implements control so as to stop the light emissionby the light emission unit once light in the light quantity has beenemitted.
 20. An image-capturing system according to claim 14, wherein:the light emission control unit in the illumination device hasinformation indicating drive current and light emission intensitycharacteristics at the light emission unit.
 21. An illumination systemconstituting an image-capturing system according to claim
 14. 22. Acamera having an image-capturing device constituting an image-capturingsystem according to claim
 14. 23. An image-capturing system according toclaim 14, wherein: the image-capturing system is a camera.
 24. Animage-capturing system according to claim 14, wherein: theimage-capturing system is a portable device equipped with a camera.